Nitride and polysilicon interface with titanium layer

Abstract

A conductive structure in an integrated circuit (12), and a method of forming the structure, is provided that includes a polysilicon layer (30), a thin layer containing titanium over the polysilicon, a tungsten nitride layer (34) over the titanium-containing layer and a tungsten layer over the tungsten nitride layer. The structure also includes a silicon nitride interfacial region (38) between the polysilicon layer and the titanium-containing layer. The structure withstands high-temperature processing without substantial formation of metal silicides in the polysilicon layer (30) and the tungsten layer (32), and provides low interface resistance between the tungsten layer and the polysilicon layer.

Description

[0001] This application is a continuation of co-pending International Application No. PCT / US2003 / 029085, filed Sep. 16, 2003, which designated the United States and was published in English, and which claims priority to U.S. Provisional Patent Application No. 60 / 411,710, filed Sep. 18, 2002, both of which applications are incorporated herein by reference.TECHNICAL FIELD [0002] The present invention relates to conductive structures used in semiconductor devices and to methods of manufacturing the same. BACKGROUND [0003] Polycrystalline silicon or “polysilicon” structures are commonly used as conductive elements in integrated circuits. [0004] For example, in memories and other devices, an oxide-insulating layer overlies the channel region of a field effect transistor (“FET”) and a conductive polysilicon layer overlying the oxide layer serves as the gate of the FET. The amount of electrical charge on the gate controls the conductivity through the channel region of the FET. Thus, the sp...

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Benefits of technology

[0046] The high temperature processing step also serves to anneal the other elements of the structure and to reduce the resistivity of the structure. For example, a structure incorporating a 1 nm titanium interface metal layer, a 16 nm tungsten nitride layer and a 40 nm tungsten conductor metal layer has a sheet resistance of about 10 ohms per square as deposited and about 4 to about 5 ohms per square after high temperature processing. The same structure has an interface resistance of about 70 Ω-μm2 after high temperature processing. By contrast, a comparable structure without the titanium layer has an interface resistivity of about 5,000-10,000 Ω-μm2 after high temperature processing.

[0047] A further advantage of structures according to preferred embodiments of the present invention is that such structures including the titanium interfacial metal are substantially stable when exposed to an oxidizing gas mixture of water vapor and hydrogen as, for example, exposure to such a mixture with respective relative mole fractions of 10% and 90% at an elevated temperature of above about 900° C.

Problems solved by technology

The layer including the interface metal, as deposited, desirably is relatively poor in nitrogen.

However, the structure, after high temperature processing, has an interface resistance substantially lower than a comparable structure with a metal nitride layer but without the interface metal.

It is believed that this, in turn, leads to a lower interface resistance than would occur in the ab

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